"Breeding-back" aims to restore or immitate extinct animals by selective breeding. This blog provides general information, the facts behind myths and news from various projects.

Friday, 7 February 2014

Is the Exmoor less unique than we used to think?

A lot of
Exmoor pony fanciers and also some people involved in rewilding consider the
Exmoor pony the horse breed that is closest to the original European wild horse
or even a surviving wild, undomesticated population [1]. And in my last post on
this breed, I praised the Exmoor as the only virtually pure member of a feral
pony type I called the “British primitive horse” that allegedly was the
ancestor of many other native British horse breeds. A very interesting and
well-sourced document I came across thanks to the Blogger user “Unknown” provides
information that the Exmoor pony may be not as special as I and a lot of other
people used to think.

Let’s start
right from the beginning: the far-fetched claim that the Exmoor pony is a
surviving wild horse has to be discarded because of paleontological and genetic
data. Wild horses died out on the British isle at the end of the Mesolithic,
and no equines are present in the archaezoological record of the island until
domestic horses were introduced by the Celts [1,2,3]. Exmoor supporters claim
that this is the case because the wild horses retreated into mountainous areas
where fossilization is less likely, so that they might not have left a trace in
the record [1]. But this is a mere speculation.

Genetically,
the Exmoor pony is seemingly not set apart from other domestic horses. I am going
to simply quote myself now (references below) so that I don’t have to repeat
myself:

Inclusion of wild mares into domestic
stock all over Europe is very probable for whole Europe based on the genetic
evidence [2,3,4] and the fact that wild stallions are
virtually intractable is probably the reason why only very few of them were
used in domestication and therefore why domestic horses have such few Y
chromosome variants. An Y haplotype or a complete Y chromosome not present in
any other horse lineages would therefore be a very strong indication of local
introgression in a breed (and a very high Y diversity in a domestic horse
population would thus imply very strong introgression or even descendant
from local wild horses). A 2004 study [4] showed that a large number of breeds have the same few Y chromosomes,
including the Exmoor (and therefore ruling out that it descends from British
wild horses or that it experienced much, not sex-biased local introgression)

Even more
interestingly, Cieslak et al. 2010 examined mitochondrial haplotypes of
predomestic and domestic horses. 87 haplotypes were recognized, 30% of them
were found to be still present in modern domestic horses [5]. And the
distribution of these haplotypes within the Eurasian horse population is not
surprising assuming that all or most horses were domesticated in the Eurasian
steppe. In the east, the number of retained predomestic haplotypes are much
higher (Arabian 18, Akhal Teke 13) than of those in the far west of the
continent (Fjord 5, Exmoor and Welsh 2). This is what is to be expected if the
population was continuously inflated and fragmented during the expansion
westwards [5]. The very low number of predomestic haplotypes detected in the
Exmoor and its relative is especially revealing. Although it is possible that
this was the result severe bottlenecks [2], anthropogenic or not, a conclusive
indication for a genetic relationship of the Exmoor with western European wild
horses special among other European horse breeds is still lacking.

The fact
that all contemporary Exmoors display various shades of bay and brown and no
other colours, that most of them have very prominent countershading and mealy
mouth, and that only very few of them have white spots, is interpreted as
evidence that the Exmoor is a wild horse-like animal with little intermixing
with domestic horses by advocates because most wild animal populations have a
stable phenotype [1]. But in fact there is no conclusive evidence that the
Exmoors had a uniform phenotype prior to the bottleneck events and artificial selection
– actually there are hints for the contrary [2]. Apparently the horses always
were small, but there are no helpful references on the colours within the
population over the time prior to the 18th century. Between 1805 and
1809, 81 Exmoor ponies were sold from the moor (a sample which might be of
sufficient size) and their colours were documented. 33 were black, 19 were
grey, 17 were bay, 9 were dun, 2 were chestnut and one was piebald [2]. It is
argued that animals with non-Exmoor influence were captured from the more to
maintain the alleged purity of the population, but there is no evidence for
such an intention and since there is no earlier evidence for the colour of the
horses/ponies at Exmoor, it simply cannot be said whether individuals displaying
these colours were “pure” or “non-pure” [2]. Two illustrations in the
Illustrated London News from 1835 show the capture of free-ranging Exmoors;
these clearly show horses with long manes, their colour is either brown with a
white blaze and a white “sock” or grey (one portrayed horse might be black)
[2]. A chestnut stallion is mentioned as well. At this time, crosses with the
Thoroughbred and Arab horse were present in the moor, so the portrayed horses
could indeed be the results of intermixing [2]. However, the portrayed colours
are in accordance with those described from the sales between 1805 and 1809,
and they are not a support for the contemporary colour of the Exmoor pony having
been present homogeneously in the population prior to the 20th
century either. The notion made by Worthley Axe in the year 1906 is also
interesting: “…the majority of so-called
Exmoors are simply mongrels” [2]. 1860 some the larger members of the horse
population at Exmoor were captured to be used as packhorses [2], I interpret
that this means there also was size variation in the Exmoor pony back this
time. The Acland herd, which made a considerable contribution to the modern
Exmoor population, also had a number of greys in the herd in the year 1900. There
is a record that suggests that they started to select out black Exmoors because
they lacked the mealy mouth, indicating that this herd was artificially
selected for this trait [2].

Dartmoor ponies. Some of the older Exmoor pony herds might have looked like this.

Postcranial
bone material of Pleistocene horses has been compared with the Exmoor pony, and
good matches have been found [1]. The problem with these comparisons, apart
from the limited samples, is that the variation within predomestic and domestic
horses is that large that they can hardly be distinguished only on the basis of
their bones [2]. Furthermore, since the Exmoor is one of the “primitive breeds”,
it is not surprising that an osteologic match has been found, except for the
not examined skull material.

There are
colour matches between the modern Exmoor population and wild horses.
Countershading and mealy mouth are an ancestral trait, as is the bay base
colour [6]. However, the presence of the allele for sooty bay/brown has yet to
be confirmed in wild horses, and the lack of dun might not be a primitive
character in European wild horses (see here), but there are cave paintings that
look like they portray non-dun horses (see here and here), and the dun factor
was not yet tested in predomestic horse populations [6], so I cannot rule it
out and won’t use it as an argument against the Exmoor. But a colour match
between a horse breed and their wild counterparts no way indicates either a
close relationship nor direct descent or even that this breed is predomestic, neither
do the other phenotypic matches regarding bodily proportions or the short mane.
Have a look at how many dog, sheep or goat breeds show the colour of their wild
type, and look at their resemblance in other optical features (examples here,
here [ wildtype colour, yet clearly domestic] and here). Also the hardiness and wild behaviour under natural conditions
does not necessarily endorse the view that the Exmoor is closer to the wild
European horse than other breeds; ecologic and behavioural resembling wild
animals is, not surprisingly, a feature of many landraces and can either be
retained traits or secondarily developed traits because of their exposure to
natural selection. Furthermore, mind that those primitive, less-derived
features of the Exmoor are not unique to this breed (but that is not an
argument against its purported primitive status of course).

You might
remember my earlier post in which I adopted Sue Bakers proposal [1] that the
Exmoor ponies represent the only virtually pure members of a primitive feral
horse type that is ancestral to all other sturdy British landraces. This
article made me rethinking this assumption; if the Exmoor always had a more or
less heterogeneous phenotype prior to the 20th century, and since
related landraces like the New Forest pony, Dartmoor Pony and others are
heterogeneous today and there is no evidence either that they were
homogeneously brown/bay with white muzzle before their evident intermixture
with other breeds, it is more parsimonious that the Exmoor probably never was
homogeneous in the past and nor that the original stock introduced by the Celts
was.

Another
possibility is they originally were indeed homogeneous but intermixture with
other domestic horses had taken place before the documenting of their colours
started to take place. Furthermore, intermixture with derived horse breeds like
the Arab and the Thoroughbred evidently took place at in the late 19th
century [2] and the modern homogeneous phenotype of the Exmoor apparently is a product
of artificial selection. First of all, we know that the Exmoor went through
several human-caused bottleneck events [1,2,3], and that it was selected for
its bay/brown coat with countershading and mealy mouth right from the late 19th
century till today [2]. It might surprise you that black and grey actually were
permitted colours at the beginning of systematic Exmoor pony breeding with the
formation of the Exmoor Pony Society in 1921 [2]. This shows that there must
have been animals with such colours appearing in the population at that time,
and that artificial selection purged them out. Additionally, white markings
must have been present too, because they still appear today, albeit only
rarely.

Iberian
breeds that bear a certain similarity to the Exmoor, like the Garrano, Asturcon
or Pottoka could be used an argument for the hypothesis that both those pony
groups descend from a western European wild horse type that was separated when
the English channel emerged and that looked like the British and Iberian
ponies. However, this hypothesis is far-fetched when considering the
aforementioned gap of equines in subfossil record of Great Britain. The
mainland ponies must have been the base for the ponies the Celts introduced to
the British isle, and there was exchange of culture and goods between Great
Britain and Iberia during the bronze age and antiquity. Therefore it is in my
opinion not surprising that the ponies of Iberia and Great Britain look alike,
and no hypothesis of local ancestry from wild horses that is not supported,
even contradicted by genetic data is necessary. Furthermore, it is important to
know that the use of British ponies such as the Exmoor on breeds like the
Pottoka during the 20th century is well-documented [7], although I
think it must not be the case in all Exmoor-like northern Iberian landraces.

The
hypothesis that the Exmoor pony is strongly influenced by western European wild
horses or even a surviving wild horse population seems to be zoologically untenable.
And this is the reason why the Exmoor is “just a breed” from zoological
perspective and not listed as a wild representative of Equusferus as the
Przewalski by zoologists – not because they are “conservative” or have preconceptions.

It seems, or
is at least likely based on the historic and genetic evidence, that the Exmoor
is a mix of local ponies of Celtic origins, and probably did not have a uniform
appearance prior to artificial selection in the 20th century. Intermixture
with more-derived horses probably was always there and is documented for the
late 19th century. This is, in my view, actually similar to the
nature of the Konik, although the Konik/Panje horse has no known
feral/semi-feral history. Intermixture now is a problem for the pedigree of the
horses in the moor again because non-Exmoor horses somehow got into the moor
and interbreed freely with them [2].

That all is
not to say that the Exmoor is not useful for ecologically substituting the wild
horse in Europe, far from it. The Exmoor, with its sturdy and strong body,
thick head and short mane, still has a “functional phenotype” resembling what
we assume for the European wild horse (although the lack of dun, as outlined
above, might not be an ancestral trait). Furthermore, its feral or semi-feral
history made it retain or redevelop useful behavioural traits such as shyness
towards humans and effective defensive behaviour against predators and a very
hardy nature (not unique to the Exmoor, though). Therefore it is good that many
rewilding projects use the Exmoor, although I think that a more diverse set of
breeds should be used in whole Europe, what apparently is the case.

The article
is really refreshing as it re-investigates the merely anecdotic evidence
regarding wide-held opinions on this breed and its relations to the predomestic
western European wild horse and provides a new approach to this breed. It shows
that the study of extinct animals keeps being exciting when new data emerges or
considerate revisions are done.

Hi there,There is strong evidence that the Iberian Exmoor type horses have Celtic origin or at least strong Celtic influence, the Celtic culture was predominant in all Western Iberia until the first centuries of our present time surviving in the NW all the period of Roman domination. One of many examples is the word Garrano (type of small horse from NW of Iberia), this word has Celtic origin as many others in the region and one can still find similar or equivalent words in the modern Celtic languages like the Irish "gearr" that means short or small :)

About this blog

This blog is on everything related to the so-called “breeding-back” of extinct animals: From the extinct animals themselves, over their often domestic descendants and dedomestication to news and facts about various breeding-back projects, reports and photos from my own breeding-back related trips. I try to have a balanced and fact-based approach to this subject and to dismantle many of the popular myths. Enjoy!

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About me

I am an Austrian student of biology/zoology at the University of Vienna. My major interest always have been extinct animals, from dinosaurs to Pleistocene megafauna and more recent extinctions. Besides that I am interested in evolution, genetics and ecology.
I am also an amateur animal artist, making drawings and models mostly of extinct animals.